Anaemic conditions may occur as a result of losses of blood from an individual or as a result of insufficient supply of bioavailable iron in the diet. In this respect, a particular problem exists in the pig industry. Newborn piglets have a total body reservoir of iron which is about 50 mg. During the first 2-3 weeks of life (the suckling period) their weight gain is so rapid that the daily requirement for iron is about 7-10 mg in order to maintain a physiologically normal level of haemoglobin in their blood, i.e. about 90-120 g per 1. However, the daily supply of iron from the sow's milk is only about 1 mg and inevitably, a serious and often fatal, anaemic condition will occur within a few days after birth, if a supplementary iron supply is not provided.
Presently, such a supplementary supply of iron is normally provided by giving newborn piglets an injection of an iron-containing substance such as an iron dextran. Obviously, this method of supplying iron is very labour-consuming and in addition it involves a risk of spreading infectious microorganisms via the injection needle and of causing a stress condition in the animals.
It is therefore not surprising that several attempts have been made to provide iron-containing compositions which by oral administration to suckling piglets might supplement their insufficient supply of iron.
A general problem associated with oral administration to suckling animals of iron-containing compositions is the fact that their energy requirements is substantially covered via the mother's milk and hence they show no willingness to ingest more than a few grammes of solid sources of nutrients and in addition, suckling animals are extremely selective with regard to which solid materials they are willing to ingest.
Sources of iron in oral compositions may be organic or inorganic iron salts or compounds containing chelated iron or complex-bound iron ions. When selecting a suitable iron source for an oral composition, several factors must be taken into account. Whereas it may be advantageous to include an iron source with a high solubility and hence a high degree of bioavailability, at the conditions prevailing in the gastrointestinal tract in order to provide a required dosage at a low amount of the iron-containing composition, such a high solubility may at the same time render the composition so unpalatable that a voluntary ingestion in sufficient amounts by suckling animals, is not obtainable.
Alternatively, it may be attempted to include an iron source having a low solubility and a low degree of bioavailability under gastrointestinal conditions, including those of the oral cavity, whereby the iron-containing composition might become more palatable. In general, however, such an approach would require the administration of amounts of the iron-containing composition exceeding those which may be voluntarily ingested by suckling animals in order to provide a physiologically sufficient iron dosage. In addition, even compositions containing such sparingly soluble iron compounds may not have an acceptable palatability for the suckling animals.
In DE 21 11 638 is disclosed a composition containing iron polysaccharide complexes which is recommended for oral administration to suckling piglets during the first day of life. However, the composition has to be administered by introduction of the composition into the oral cavity in the form of a suspension (by use of a pistol), tablets, capsules, a paste or an aerosol.
There has also been introduced solid iron-containing compositions, e.g. containing ferrous fumarate, which may be ingested voluntarily by suckling animals. However, these known compositions contain iron which is in a form where less than 10% is absorbable and furthermore, in order to provide these known compositions in a sufficiently palatable form, it is required to incorporate relatively low concentrations of iron, such as 10 wt %. Accordingly, a suckling piglet must ingest about 80 grammes during the first two weeks of life in order to avoid anaemia. A number of suckling piglets may not be willing to ingest such a high amount of the composition.
In this context, it is also likely that the requirement to administer the above rather high amounts of an oral iron-supplementing composition is due to an inappropriately large particle size of the selected iron compound. It is known that the iron bioavailability, i.e. the proportion of the iron which can be absorbed from the intestinal mucosal membranes, depends on several factors including the intestinal pH and the particle size. In suckling piglets, the intestinal pH is typically in the range of 4.5 to 6.5. Within this pH range, the solubility of several organic iron compounds including ferrous fumarate is relatively low. Therefore, the incorporation of sparingly soluble iron salts in the form of large particles may result in a low bioavailability of iron in suckling animals.
This problem of reduced bioavailability may be solved by to providing the iron in the form of compounds having a small particle size. However, the use of ferrous compounds which are preferred since their bioavailability is generally higher than that of corresponding ferric compounds as small particles in the form of small particles gives rise to a new problem, viz. an acceleration of oxidation of the ferrous compound to ferric compound.
As an alternative to the above direct oral administration to suckling animals of iron-containing compositions it has been suggested to supply a solution of an organic iron compound via automated drinking systems and it has been found that adequate amounts of iron may be taken up by the animals via this route of administration. However, it is required to clean the drinking systems on a daily basis and besides, there is a considerable waste of the iron-containing preparation which may add unacceptably to the costs of such an administration.
It is obvious from the above that a need exists to provide a solid iron-containing composition for the prevention and treatment of anaemic conditions, in particular in suckling animals, which can be administered orally without any manipulation of individual animals and which cost-effectively secures a physiologically normal haemoglobin concentration during periods where the normal dietary iron supply is inadequate.
The present invention provides such an oral iron-containing composition which comprises the iron in a highly bioavailable form and which provides the iron in a palatable form so as to allow the composition to be voluntarily ingested by suckling animals including piglets, in sufficient amounts to maintain the physiologically normal level of haemoglobin.